from wxPython.wx import *

class MiaApp(wxApp):
    def OnInit(self):
        frame = wxFrame(None, -1, "Ciao mondo")
        frame.Show(1)
        self.SetTopWindow(frame)

        dlg = wxDialog(frame, -1, "Finestra di dialogo")
        dlg.ShowModal()
        return 1

app = MiaApp()
app.MainLoop()